Conventionally known is a domestic fuel cell cogeneration system including: an electric power generator utilizing a fuel cell; and a hot water tank configured to store water (hot water) heated by utilizing heat generated when the electric power generator generates electric power. The fuel cell used in the fuel cell cogeneration system includes a cell stack body formed by stacking plate-shaped cells. An electrode is provided at a center portion of the cell, and respective manifold holes, such as a fuel gas supplying manifold hole, are generally formed at a peripheral portion of the cell. When the cells are stacked, respective manifold holes are connected to one another to form respective manifolds, such as a fuel gas supplying manifold.
As above, since the manifolds are formed at the peripheral portion in the fuel cell, the heat is easily released from a cooling medium, which has recovered the heat, to the atmosphere. Therefore, in order to reduce the heat release from the fuel cell, known are a fuel cell (see PTLs 1 and 2, for example) in which a heat insulating member is arranged outside the fuel cell stack and a fuel cell (see PTL 3, for example) in which the fuel cell stack is contained in a closed container, and an internal space of the closed container is filled with an electrically insulating liquid.